Genetic Toolbox: Part 1
By: John Maday
As bull-sale season begins, NCBA webinar focuses on genetic selection, highlighting an old tool; crossbreeding, and a newer tool; genomic testing.
A recent webinar from NCBA’s Producer Education program outlined how cow-calf producers can take steps to accelerate genetic improvement in their cattle and position their herds for future profitability and sustainability.
The webinar featured Kansas State University Cow-Calf Extension Specialist Bob Weaber, PhD, who also serves as faculty coordinator of the K-State’s Purebred Unit, and University of Missouri animal scientist and Beef Genetics Extension Specialist Jared Decker, PhD. This article focuses on Dr. Weaber’s presentation on the role of heterosis, and part 2 of this series will summarize Dr. Decker’s presentation on the use of genomic tools in commercial cow-calf operations.
Weaber notes that commercial cow-calf producers face a variety of goals influencing their genetic-selection decisions, including production efficiency, profitability, end-product quality and sustainability. Heterosis gained through a planned crossbreeding program can help address several of those goals, he says.
Genetic selection tools, including use expected progeny differences (EPDs), section indexes and heterosis provide key opportunities for augmenting production efficiency at the cow-calf level, Weaber says. He acknowledges that produces face the question of whether the benefits of straight breeding for economically important traits outweigh the improvements in lowly heritable traits gained through crossbreeding, particularly maternal traits. Producers should, he says, select for additive and non-additive genetic merit, noting that use of EPDs can bring improvements in some traits such as those for growth and carcass merit, while crossbreeding helps address lowly heritable traits such as those influencing reproduction, fertility and cow longevity in the herd.
Weaber points out that crossing more divergent parent lines results in more heterosis. Crossing Bos taurus cattle with Bos indicus, for example, results in higher levels of heterosis in F1 (first-generation) calves than crossing two Bos taurus breeds. Crossing between two Bos taurus breeds, however, results in significantly higher F1 heterosis than any within-breed cross, even though some breeds have become more phenotypically similar.
In addition to heterosis, Weaber points out that crossbreeding also can offer the benefits of breed complementarity. This allows producers to capitalize on the strengths of two or more breeds, while minimizing each breed’s weaknesses.
Weaber also notes that recent genomics research has shown that within breeds and individual animals, “broken” or nonfunctioning genes which, when expressed, can result in embryonic loss or other undesirable defects. The locations of these broken genes often are breed specific, and crossbreeding, Weaber says, can reduce their impact on offspring. If the sire has broken genes and the dam has functional genes at same loci, progeny will inherit one good copy of the gene which, if dominant, prevents expression of the damaged gene.
Crossbred calves tend to be more vigorous and faster-growing than similar straight-bred calves, with about a 4 percent advantage in weaning weights, but Weaber says the greatest long-term benefits of crossbreeding come from maintaining a crossbred cow herd.
On average, Weaber says, crossbreeding in the cow herd results in a 16% improvement in longevity, meaning each cow produces an average of one more calf over her lifetime. This means producers can reduce costs by raising fewer replacement heifers each year and increase revenue by selling more heifers.
To illustrate the potential economic benefits of crossbreeding, Weaber provides an example of a 100-cow herd with an 80% weaning rate and 575-pound average weaning weight projected over a 10-year period.
Over those 10 years, a 6% improvement in calf survival to weaning equals 48 more calves to sell. A 4% improvement in average weaning weights adds up to 18,400 pounds of additional sale weight over 10 years. Combining the benefits of crossbreeding on weaning weight and rate results in 105,800 estra pounds weaned per cow exposed over that 10-year period. Overall in this example, Weaber says heterosis adds value of about $200 per cow per year at $2 per hundredweight (cwt) for 500- to 600-pound calves. Breakeven price is reduced by $0.37 per pound, meaning straightbred calves would need to generate premiums of $264 per head, such as through breed-based marketing programs to equal returns from crossbreeding.
Goals in a crossbreeding system should include:
· Optimizing calf and maternal heterosis.
· Use breed complementarity to match cows to their environment and calves to the market.
· Minimize variability in calves by stabilizing breed inputs.
· Use advanced reproductive technologies such as estrus synchronization and artificial insemination to help structure mating systems.
For producers who retain heifers from their own herd for breeding, retaining heterosis in the cow herd becomes an additional goal. In a typical crossbreeding system, F1 calves will display the highest level of heterosis. Mating the same crossbred sires with resulting crossbred heifers will result in lower levels of heterosis in their offspring, but some hetrosis is retained in future generations.
Depending on their herd size, production environment and marketing goals, producers can retain heterosis in the cow herd either by rotating bull breeds, using hybrid or composite bulls or by purchasing replacement heifers and selecting bulls for a terminal-cross system focused on calf performance and carcass value rather than maternal traits.
Build a breeding plan with attainable goals based on intended market end points, your production environment and management practices, Weaber says. And stick to it.
For a wealth of information on genetic selection and breeding systems, Weaber suggests producers use the Beef Sire Selection Manual, available online from the National Beef Cattle Evaluation Consortium (NBCEC).
Weaber also notes that Kansas State University will host the annual Beef Improvement Federation (BIF) conference in Manhattan this summer, from June 14 through June 17, featuring cutting-edge discussions on genetic improvements toward future profitability in beef production. Learn more at beefimprovement.org.